What a wonderful little anecdote! That was Brian, all right.

Phil Karn, KA9Q

ABSOLUTELY! The first thing I do with any new OS is to map the caps lock key to the control key.

I can actually think of a practical use for this, if it could be made really lightweight.

I work with groups that fly small, long-duration stratospheric balloons with ham radio beacons. The payload weight budget is too small (15 grams) for batteries, and even with them the extremely low temperatures would be a problem. Supercaps work well at low temperatures, but energy densities are too poor to store enough energy for an entire night. So the payload only operates during the daytime from two thin-film solar cells.

I've been wracking my brain trying to think of another source of ambient energy (besides sunlight) that could be harvested. Even a few milliwatts could be useful, accumulated in a supercap until there's enough energy for one GPS fix and radio transmission cycle. Harvesting broadcast radio stations is one idea, but that only works near population centers. I'd thought of some sort of heat engine working between the warm earth below and the cold sky above, but did not know if it was at all practical. Maybe it still isn't, but it's an interesting idea.

Part of the introduction is missing:

After "Plenty of cat owners will happily tell you their felines are capable of responding to their own names"

it should read "...they just choose not to."

There, fixed that for ya.

Ah, so *THIS* is how the Talosians kept Captain Pike from bouncing off the walls of his cage. I always wondered about that.

I don't think it would be as hard as you might think PROVIDED you really understood it yourself. Of course, this applies to anything you wish to teach to anyone.

The problem with relativity is that it is so counter intuitive to everyday experience and to the classical physics you've been taught that you have to unlearn much of it first. That may make it easier for younger people to understand -- they don't have as much to overcome as they would later.

Like most EEs, I was taught classical electromagnetism, first in high school, then in lower level undergraduate physics, and finally in much more detail in junior level EE school classes. We were also taught relativity, but as a separate topic within physics. Had I been taught relativity first, and then been taught electromagnetism in the relativistic way I think it would have actually have been easier and more satisfying. I would have learned that there really isn't such a thing as "magnetism"; what we see as magnetism is really just the electrostatic force as affected by special relativity (and some quantum mechanics). I would have readily understood why there are no magnetic monopoles, for example. And it would have shown me how every field in physics is related to every other, in fact that there really is only one "physics".

Actually no, it's not a straightforward calculation. That's why they want to conduct the test.

It's not a simple collision like we learned about in physics class, with the change in the asteroid's momentum coming entirely from the impactor. The impactor will hit at extremely high velocity (by earth standards), meaning that it will carry a lot of kinetic energy (one half mass times velocity squared) in a small volume. This kinetic energy will vaporize and blow off part of the asteroid, which because of the asteroid's small size, will completely escape.

The mass of the ejecta will greatly exceed the mass of the impactor, so even though it may move much more slowly than the impactor it will carry away considerably more momentum (mass times velocity). The momentum of this ejecta will have most of the effect on the asteroid's trajectory.

But it's unknown exactly how much momentum will be carried away by the ejecta as this depends on the makeup of the asteroid, its density, porosity, how quickly the impactor stops and releases its energy, etc. So that's why they want to try it.

A similar effect was at play in the JFK assassination that helped cause the counter-intuitive "back and to the right" motion of his head that had so many people incorrectly thinking there was a second shooter.

The largest estimate for the size of Psyche is 253 km across. Mars is about 6800 km in diameter, enormously larger.

Yes, I just picked up a SDRPlay 2 last weekend.

The main differences between it and the Funcube dongle are the same: the SDRPlay can sample at much higher rates, but only at 12 bits/sample, while the Funcube dongle samples at 192 kHz with 16 bits. The Funcube dongle therefore appears better suited to narrower modes, especially on HF and VHF where there may be strong interferers on nearby frequencies. The SDRPlay can do broadband modes too wide for the Funcube, such as HD Radio, ADS-B and digital TV, though many of those can also be done even more cheaply with 8-bit RTL-SDR dongles. The SDRPlay can also produce wideband waterfall displays.

Many hams today ARE using the Raspberry Pi and Arduino for their projects. Such as the local high school kids I help mentor. They build high altitude balloon payloads and fly them, and they all carried either an Arduino, a Pi, or both.

I/Q interfaces are vulnerable to ground loops only if the I/Q interface is analog. Why should it be, when we have excellent digital interfaces designed specifically for stereo digital audio? There are now several inexpensive SDRs (price range $100-$200) with USB interfaces, e.g., the Funcube Dongle Pro+ and the SDRPlay (there's now a second version). There's also the ultra-cheap RTL-SDR, but its narrow 8-bit A/D limits its use to VHF or UHF signals without strong adjacent channel interference. It's ideal for ADS-B (with a filter!) but I wouldn't recommend it for HF.

I've done most of my work so far with the Funcube dongle, which samples at 192 kHz and 16 bits/channel, feeding a USB interface. It looks just like a standard audio A/D to the OS, because that's what it is. The I&Q signals are produced at baseband so yes there are DC offsets and small gain and phase errors, but I found them easy to remove in software. Some phase noise is sometimes audible within a few hundred hertz of DC, but is easily swamped by typical input noise and gain settings.

Overall, this thing makes an excellent but inexpensive general coverage receiver. I sure wish I had something like this when I was a young ham without much money.

You're welcome!

Hey, if you can read that disk, could you put it on the net somewhere? I didn't keep copies of all the earlier versions of my software. It'd be neat to see which one you got.

Probably the ultimate in QRP right now is WSPR (Weak Signal Propagation Reporter). This is a specially-designed very low speed (~1 bps) digital modulation and coding format designed for use as a propagation beacon, especially on the HF ("shortwave") bands. But it has recently been adapted for tracking ultra light weight (12.5 gram!) high altitude balloon payloads. One such payload, WB8ELK-2, has completed three complete trips around the world in the past month and is now on its fourth:

https://tracker.habhub.org/#!m...

The tracker payload is powered directly by a pair of small thin-film solar panels. The weight budget is so extremely tight that there is no battery, so it transmits only during the day.

Well, not to toot my own horn too loudly, but in the mid 1980s I wrote a TCP/IP implementation. I intended it for ham radio use on low end PCs, as the only existing general purpose implementations were on commercial minicomputers far beyond a ham budget. (I actually began it on a dare by Terry Fox, WB4JFI, who insisted it was too complex to implement on anything a ham could afford.)

Before I knew it, my software was being widely used outside ham radio for dialup access to the Internet. Universities and companies set up banks of modems and PCs to give their students and employees access to their existing connections. Pretty soon commercial companies sprang up to do the same for the public, again using my software; I think we now call them "Internet Service Providers".

Meanwhile, the OSI world was continuing to produce large piles of paper, but no inexpensive (or free), usable software.

In the early 1990s, I went to Qualcomm where I ported my code onto their phones so it could be used to provide wireless Internet services.

Sure, my software is long obsolete now. When people still ask about it, I tell them to go look at Linux. But it once played a role that went well beyond ham radio, even though that's all I had originally meant it for. Perhaps this was an example of a butterfly flapping its wings; I don't know.

Thanks. It was actually TCP/IP (the Internet protocols) over packet radio.